| .MESA | OpenGL | Fişiere de date | OpenGL GLUT File | GLUT | Silicon Graphics, Inc. |
| .MESSAGE | WebSTAR | Fişiere de date | WebSTAR Directory Indexer Message | WebSTAR | Kerio Technologies |
| .MESSAGES | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MET | Emulex Corporation | Fişiere de date | eMule Resource File | eMule | Open Source |
| .METAL | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MEU | Microsoft Corporation | Fişiere de date | DOS Shell Menu Group File | MS-DOS | Microsoft Corporation |
| .MEX | MathWorks | Fişiere de date | MATLAB Dynamically Linked Subroutine File | The MathWorks MATLAB | MathWorks |
| .MEZ | MusicEase Software | Fişiere de date | MusicEase Document File | MusicEase | MusicEase Software |
| .MFA | Clickteam | Fişiere de date | Multimedia Fusion Development File | Multimedia Fusion | Interscape |
| .MFD | Yamaha Corporation | Fişiere de date | Music Finder Database | MusicFinderView | PSR Tutorial |
| .MFI | Microsoft Corporation | Fişiere de date | Windows 98 Resource Kit Data Format | Microsoft Windows | Microsoft Corporation |
| .MFJ | Jarrold Group - Physical and Analytical Chemistry | Fişiere de date | MOBCAL Data File | MOBCAL | Jarrold Group - Physical and Analytical Chemistry |
| .MFL | Verity Software House | Fişiere de date | ModFit LT Analysis Report File | ModFit LT | Verity Software House |
| .MFO | Perl Express Group | Fişiere de date | Perl ModInfo Descriptor File | Perl | Larry Wall |
| .MFR | Autodesk, Inc. | Fişiere de date | Autodesk Moldflow Result Data | Moldflow Communicator | Autodesk, Inc. |
| .MFT | Kaspersky Lab | Fişiere de date | Kaspersky File Table | Kaspersky Anti-Virus | Kaspersky Lab |
| .MFU | MobileFrame | Fişiere de date | MobileFrame Update File | MobileFrame Desktop | MobileFrame |
| .MGC | Microsoft Corporation | Fişiere de date | Microsoft Clip Organizer Media Catalog | Microsoft Office | Microsoft Corporation |
| .MGD | Maxium Developments Inc. | Fişiere de date | Master Grade Gradebook | Master Grad | Maxium Developments Inc. |
| .MGP | Adobe Systems Incorporated | Fişiere de date | Adobe Captivate MenuBuilder Data | Adobe Captivate | Adobe Systems Incorporated |
| .MGR | Unknown Developer | Fişiere de date | MGR Bitmap | XnView MP | XnSoft |
| .MGW | Unknown Developer | Fişiere de date | Microgateway Policy Implementation Data | Microgateway | Unknown Developer |
| .MHP | Open Source | Fişiere de date | Maths Helper Plus File | Maths Helper Plus | Open Source |
| .MHX | Fujitsu Limited | Fişiere de date | Fujitsu MicroController Firmware | Fujitsu microcontroller devices. | Fujitsu Limited |
| .MICE | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MIF | Adobe Systems Incorporated | Fişiere de date | FrameMaker Interchange Format File | Adobe FrameMaker | Adobe Systems Incorporated |
| .MIO | Open Source | Fişiere de date | MioEngine Application File | MioFactory | Open Source |
| .MISC | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MJ3 | id Software | Fişiere de date | Id Software Online Sale File | Doom | id Software |
| .MJG | Bitdefender | Fişiere de date | Trojan Data | AVG Antivirus | AVG Technologies |
| .MJK | Konyisoft | Fişiere de date | Question File | Nosza, legyél má' te is MILIJOMOS! | Konyisoft |
| .MJM | Unknown Developer | Fişiere de date | JDF Data Exchange Format | Unknown Software | Unknown Developer |
| .MJR | JRiver | Fişiere de date | Media Jukebox Registration Data | Media Jukebox | JRiver |
| .MKR | Microsoft Corporation | Fişiere de date | Train Simulator Marker File | Microsoft Train Simulator | Kuju Entertainment |
| .MKS | Matroska | Fişiere de date | Matroska Elementary Stream File | The Core Media Player | Open Source |
| .ML3 | KIDASA Software, Inc. | Fişiere de date | Milestones V3 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML4 | KIDASA Software, Inc. | Fişiere de date | Milestones 4 Schedule File | Milestones Professional | KIDASA Software, Inc. |
| .ML5 | KIDASA Software, Inc. | Fişiere de date | Milestones V5 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML6 | KIDASA Software, Inc. | Fişiere de date | Professional 2000 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .ML7 | KIDASA Software, Inc. | Fişiere de date | Milestones Professional 2002 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML8 | KIDASA Software, Inc. | Fişiere de date | Milestones Professional 2004 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .ML9 | KIDASA Software, Inc. | Fişiere de date | Milestones Professional 2004 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .MLA | Unknown Developer | Fişiere de date | WorshipCenter Pro Document | WorshipCenter Pro | Interscape |
| .MLB | Avanquest Software | Fişiere de date | MyLabel Designer Deluxe Project File | MyLabel Designer Deluxe | Avanquest Software |
| .MLC | Microsoft Corporation | Fişiere de date | Microsoft Language Interface Pack | Microsoft Windows | Microsoft Corporation |
| .MLD | FMJ-Software | Fişiere de date | I-Melody Format For I-Mode | Awave Studio | FMJ-Software |
| .MLI | Unknown Developer | Fişiere de date | Encyclopedia Media List | Unknown Software | Unknown Developer |
| .MLM | Agile Molecule | Fişiere de date | MolMeccano File | Abalone | Agile Molecule |
| .MLN | Autodesk, Inc. | Fişiere de date | AutoCAD Multiline Definition Data File | Autodesk AutoCAD | Autodesk, Inc. |
| .MLP | Meridian Audio | Fişiere de date | Meridian Lossless Packing Audio File | MLP Professional Encoder Software | Meridian Audio |
| .MLS | KIDASA Software, Inc. | Fişiere de date | Milestones Simplicity File | Milestones Professional | KIDASA Software, Inc. |
| .MLT | Business Forecast Systems, Inc. | Fişiere de date | Multivariate Forecast File | Forecast Pro | Business Forecast Systems, Inc. |
| .MLTV | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MM | Kodak | Fişiere de date | Kodak EasyShare Thumbnail Cache File | Kodak EasyShare | Kodak |
| .MMA | Open Source | Fişiere de date | Master Album Maker Photo Album File | Master Album Maker Viewer | Open Source |
| .MMAP | Mindjet | Fişiere de date | MindManager Map File | MindManager | Mindjet |
| .MMB | Mediachance | Fişiere de date | MultiMedia Builder Data | MediaChance Multimedia Builder | Mediachance |
| .MMC | Microsoft Corporation | Fişiere de date | Microsoft Media Catalog | Microsoft Office | Microsoft Corporation |
| .MMD | Cumulate Labs | Fişiere de date | Cumulate Draw Editable File | Cumulate Draw | Cumulate Labs |
| .MMF | Microsoft Corporation | Fişiere de date | Microsoft Message File | Microsoft Exchange Server | Microsoft Corporation |
| .MMM | Magix Software GmbH | Fişiere de date | Music Maker Arrangement File | MAGIX Music Maker | Magix Software GmbH |
| .MMP | MixMeister Technology | Fişiere de date | MixMeister Studio Playlist | MixMeister Studio | MixMeister Technology |
| .MMR | Fuji Xerox | Fişiere de date | Fuji Xerox Fax Image | FaxSee Pro | SFaxTools |
| .MMS | Nokia | Fişiere de date | Multimedia Messaging Service Message | Nokia Suite | Nokia |
| .MMT | Open Source | Fişiere de date | Nimbus 7 SAMS Data File | Microsoft Notepad | Microsoft Corporation |
| .MN | MathWorks | Fişiere de date | MATLAB Data | The MathWorks MATLAB | MathWorks |
| .MN2 | Interplay Entertainment | Fişiere de date | Descent 2 Mission File | Interplay Descent 2 | Interplay Entertainment |
| .MN7 | Microsoft Corporation | Fişiere de date | Microsoft Money (Ver 7) Data File | Microsoft Money | Microsoft Corporation |
| .MN9 | Microsoft Corporation | Fişiere de date | Microsoft Money File | Intuit Quicken | Quicken |
| .MNC | Autodesk, Inc. | Fişiere de date | AutoCAD Compiled Menu File | Autodesk AutoCAD | Autodesk, Inc. |
| .MND | Autodesk, Inc. | Fişiere de date | AutoCAD Menu Compiler File | Autodesk AutoCAD | Autodesk, Inc. |
| .MNO | Adobe Systems Incorporated | Fişiere de date | Macromedia Design Note | Adobe Dreamweaver | Adobe Systems Incorporated |
| .MNY | Microsoft Corporation | Fişiere de date | Microsoft Money File | Intuit Quicken | Quicken |
| .MO | Dassault Systèmes | Fişiere de date | Dymola Simulation File | Dymola | Dassault Systèmes |
| .MOD | Open Source | Fişiere de date | Amiga Music Module File | ModPlug Player | Open Source |
| .MODEM | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MOHO | Smith Micro Software | Fişiere de date | Moho Animation Project | Smith Micro Moho Debut 12 | Smith Micro Software |
| .MOL | Interscape | Fişiere de date | MDL Molfile | Avogadro | Open Source |
| .MOL2 | Tripos | Fişiere de date | Tripos Mol2 Format File | Open Babel | Open Babel development team |
| .MONEY | Jumsoft | Fişiere de date | Money Data File | Jumsoft Money | Jumsoft |
| .MOOD | Open Source | Fişiere de date | Amarok Moodbar Data File | Amarok | Open Source |
| .MOP | James Stewart | Fişiere de date | MOPAC Input Format | MOPAC | James Stewart |
| .MOR | Corel | Fişiere de date | Corel Shared Writing Tools Data | Corel Paradox | Corel |
| .MOS | MamiyaLeaf | Fişiere de date | Leaf Camera RAW File | MacPhun ColorStrokes | Macphun |
| .MOT | NewTek | Fişiere de date | LightWave Motion File | LightWave 3D | NewTek |
| .MOUSE | Apple | Fişiere de date | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MOVEMON | Unknown Developer | Fişiere de date | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .MOX | Imagine That Inc. | Fişiere de date | ExtendSim Simulation Software Model | ExtendSim | Imagine That Inc. |
| .MP0 | Sony | Fişiere de date | Sony Ericsson GPEH Session | Sony Ericsson GPEH | Sony |
| .MP5 | Waterloo Maple, Inc. (Maplesoft) | Fişiere de date | Maple File | Maple | Waterloo Maple, Inc. (Maplesoft) |
| .MP6 | Unknown Developer | Fişiere de date | CS225 MP6 Huffman Encoding Text Data | Unknown Software | Unknown Developer |
| .MPCB | ReliaSoft | Fişiere de date | ReliaSoft MPC Data | ReliaSoft MPC | ReliaSoft |
| .MPD | Microsoft Corporation | Fişiere de date | Microsoft Project Database | Microsoft Office | Microsoft Corporation |
| .MPF | Microsoft Corporation | Fişiere de date | Microsoft Media Package File | Microsoft Clip Organizer | Microsoft Corporation |
| .MPH | Magix Software GmbH | Fişiere de date | Photostory Deluxe Project | MAGIX Photostory 2016 Deluxe | Magix Software GmbH |
| .MPI | Open Source | Fişiere de date | InstallJammer Project File | InstallJammer | Open Source |
| .MPJ | Minitab Inc | Fişiere de date | Minitab Project File | Minitab | Minitab Inc |
| .MPP | Microsoft Corporation | Fişiere de date | Microsoft Project File | Serena OpenProj | Serena |
| .MPQE | Blizzard Entertainment Inc. | Fişiere de date | Blizzard Encrypted Mo'PaQ File | Blizzard StarCraft 2 | Blizzard Entertainment Inc. |
| .MPR | Open Source | Fişiere de date | Bibexcel Data | BibExcel | Open Source |
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